const fn = () => 1 // ES6箭头函数, 返回值为1

let num = 3 ** 2 // ES7求幂运算符

let hasTwo = [1, 2, 3].includes(2)

let foo = function (a, b, c) {
  // ES7参数支持尾部逗号
  console.log('a:', a)
  console.log('b:', b)
  console.log('c:', c)
}
foo(1, 3, 4)

Promise.resolve().finally()
console.log(fn())
console.log(num)
console.log(hasTwo)
